The present invention is directed in general to an apparatus and method for detecting the loss of cooling air to traction motors, and more specifically to an apparatus and method comparing the predicted motor temperature (assuming a proper supply of cooling air to the traction motors) and the estimated motor temperature (as determined by certain temperature estimation processes since there are no temperature sensors on the motors) to determine whether cooling air is being supplied to the traction motors.
Alternating current (AC) traction motors are conventionally used in conjunction with electronic inverter drives to provide propulsion to locomotives, off-highway vehicles, and transit cars. These motors are generally induction motors controlled by pulse width modulating inverters. The variable frequency, variable voltage inverters are fed with direct current (DC) from a DC source or from a rectified AC source. The inverters control the amplitude and frequency of the voltage applied to the induction motors to produce the necessary motor flux and torque.
The traction motor is capable of operating outside its continuous operational envelope for a short period of time to deliver the power/torque required to meet short term loads. However, continuous operation outside these limits causes motor over-heating, which reduces motor life expectancy. It is therefore necessary to include a thermal protection system to prevent damage to the stator winding insulation system and the rotor cage of the traction motor.
Current monitoring and overload protection for rotating electrical machinery can prevent excessive overheating of the electrical winding system. Embedded winding current sensors are used in conventional thermal protection schemes, and the winding temperature is inferred from the winding current. Alternatively, rotating machines used in industrial applications employ resistance temperature detectors embedded in the stator windings to directly sense the stator winding temperatures. Whether the temperature is determined from the current flow or measured directly, the machine is shut down if the temperature rises above a predetermined threshold.
However, AC traction motors have historically not used temperature sensors to determine the actual winding temperature, because the location of the motor exposes the sensors and associated cabling to high vibration forces, impact with track and road debris and other hostile environmental conditions. The possibility of false indications or damage to the sensors creates a system reliability issue and therefore discourages the use of embedded winding sensors. However, in an effort to maintain the traction motors at an acceptable and safe temperature, cooling air is directed from a blower motor to the traction motors. The motor winding temperature is predicted based on a thermal model of the motor, and using the blower motor speed, ambient conditions, traction motor speed, current and voltage, and other parameters that can affect the traction motor temperature. Unfortunately, failure of the blower motor, a breach in the air duct directing the cooling air to the traction motors or the failure of other cooling system components may cause the motor temperature to increase to an unacceptable limit, a condition that may not be easily detected according to the prior art.